This invention relates to electronic image processing and, more particularly, to an electronic image processing system for converting character font data into image data utilizable by a raster output device capable of formatting the image data in a plurality of scan lines onto an imaging medium.
Raster output devices, such as raster output scanning devices (ROS) e.g. ROS printers, are conventionally employed to act upon a stream of video image data by traversing a predetermined raster scan pattern to create a composite image from the video image data. A ROS printer traces a raster scan similar to that of a television raster. One form of ROS printer employs a laser scanning head in a xerographic copy reproduction system. Examples of such a printer are disclosed in U.S. Pat. Nos. 3,898,627; 4,000,486; and 4,079,458.
The provision of video image data has heretofore been derived from instructions from a digital processor by arranging character representations in sequential order in the path of the raster output scanner beam and in effect taking a section through the linear character array to determine the precise bit print positions at which the raster output scanner should either print or refrain from printing. The computations necessary are performed in such a way that sequential parallel sections through the linear character arrangement are calculated scan line by scan line with the bit print instructions transmitted to the raster output scanner as soon as the determination has been made as to whether or not the scanner should print at sequentially located bit positions.
The foregoing technique places constraints on the type of printing which may be effectuated. Unless excessively large memories and computation capabilities are provided, character fonts must be specified in uniform dimensions of width and height. Only a limited repertoire of character sizes and styles are feasible for selection using conventional printing systems, and these characters must be printed at predetermined spaced intervals. In addition, conventional printing systems are relatively inflexible in that they are generally incapable of reproducing character over-strikes, truncated characters, characters of different shading, magnified and minified images, reverse field printing and other features which frequently appear in source documents or which are otherwise desirable to produce.
It would be desirable, therefore, to provide an electronic image processing system which removes the constraint of reproducing characters from uniform character fonts at predetermined spaced intervals along a scan line. It would further be desirable if characters could be printed in different shades or in reverse field without the requirement for a separate character font for each shade. It would still further be desirable to lessen the burden on the electronic image processing system relative to the acceptance and handling of "left-over" information for characters being processed. It would also be desirable to be able to write and print rectangles or "rules" without the necessity of defining and storing a character font relative thereto.